More than 70 million state-of-the-art microprocessor chips are sold each year. Each chip needs to be connected to a carrier or to the PCB directly. MCMs (Multi-Chip Modules) are high-end products requiring numerous connections for chip attachment. Bulky conventional pressure engaged connections require precious space that limits miniaturization, and prevents their use in chip attach applications.
State-of-the-art semiconductor chips entail dense structural complexity analogous to that of an entire city, all in an area of a few square centimeters. As the complexity increases, that "city" requires ever more "highways" or connections to other "cities" of the computer. The number of connections to and from a single chip can range up to a thousand, with five thousand predicted in a few years. As density increases, yield decreases, requiring that the chip or die be pre-tested. The industry requires robust, cost-effective high density solutions for pretesting dice, and for durable connections, solutions consistent with existing assembly practices.
Connections at all levels of a microelectronic system, that is from chip to board, are facing increasing challenge that results from demands in higher connection density at a lower cost. For example, "flip chip" area array solder joints for chip attach and ball grid array solder joints for connecting a chip carrier to card, can definitely increase the connection density, but often at a concomitant increase of cost per joint. Future connections need not only accommodate increased input/output (I/O) density at lower cost, but also to operate at high frequencies and under low voltages.
Flip chip technology includes any combination of techniques that directly attaches a silicon die with its active area face down to a substrate. Among these techniques, flip chip solder joint technology has been in use in the electronics industry for over thirty years. Worldwide, less than ten companies practice the flip chip solder joint technology in volume. Flip chip solder joint technology will be accelerated by strong new market drivers: use in low profile assemblies; and the proliferation of radio frequency devices. Alternatives to flip chip solder joint technology, such as conductive adhesives, are in the developmental stage. Demountable pressure engaged connections are not yet able to meet the various requirements discussed above.
At higher levels of a microelectronic system, soldered connections are also used. For example, for connecting a chip carrier or packaged chip to a printed circuit board, ball grid array (BGA) or surface mount solder joints are used. Demountable pressure engaged connections, such as the pin/socket type, are widely used for connecting a card to a board. The pin/socket type of connection, because of its bulkiness, will not be able to meet the input/output density needs of the future.
Area array flex circuit connections are being developed to replace the edge connector of a card, as a result of the demand of higher connection density. In general, pressure engaged connections are less costly compared to solder joints. However, the wider use of the former in high-end products has been inhibited also by their lower electrical and thermal stability, lack of the ability of self-assembly, and the need for large insertion force, which, when applied through the component to be attached, can result in component damage.
There have been many attempts in the prior art to achieve the low-insertion force and high contact force combination of the present invention, while maintaining miniaturization. The following examples show the range of solutions which have been tried. In all cases known to the present inventors, the connectors of the prior art have used spring action of the socket or the pins, or both. Where the pins are solid, they are straight (non-tapered), except perhaps for a rounded or pointed tip for centering.
Meuche, "EDUCATIONAL KIT FOR INSTRUCTION AND TESTING OF ELECTRICAL CIRCUITS", U.S. Pat. No. 3,008,245, uses a straight pin inserted into a socket having bumps which are plastically deformed to hold the pin in place.
Hotine, et al, "APPARATUS FOR CONNECTIONING ELEMENTS", U.S. Pat. No. 3,275,736, uses a ring having finger elements which are bent to grip a straight pin element. The elements are bent past the buckling region, then are pounded back down to grip the straight pin.
Bender, "WELDABLE FLEXIBLE CIRCUIT TERMINATION FOR HIGH TEMPERATURE APPLICATIONS", U.S. Pat. No. 5,514,839, also uses tabs extending inward to hold a straight pin element (see especially FIG. 3 a). The tabs are used as spring force elements in the bending force region, not in the buckling region.
Reimer, "PLANAR RECEPTACLE", U.S. Pat. No. 3,670,409, also uses fingers in the spring region to grip a straight pin, as does Shirling, "PIN GRID ARRAY HAVING SEPARATE POSTS AND SOCKET CONTACTS", U.S. Pat. No. 4,943,846, and others.
Evans, "METHOD OF MAKING RESILIENT PINS", U.S. Pat. No. 3,545,080, is an example of the use of pins which have spring elements. The pins are essentially straight (but for a pointed end for location), and have a spring-like section to grip straight-sided sockets.
Reymond, "SPRING BIASED TAPERED CONTACT ELEMENTS FOR ELECTRICAL CONNECTORS AND INTEGRATED CIRCUIT PACKAGES", U.S. Pat. No. 5,366,380, uses resilient contact elements which center into non-tapered holes and are pressed into place under the influence of the spring-like nature of the pins. No buckling is used, and the pin elements rest on the edge of, rather than insert into, the connection holes.
Kman et al, "PINNED MODULE", U.S. Pat. No. 5,548,486, shows the use of a straight pin with a bulged section, forced into a straight hole which is compressively deformed to grip the pin.
For a discussion of insertion force vs. contact force, see Yamada and Ueno, "Analysis of Insertion Force in Elastic/Plastic Mating", Transactions of the ASME, September 1990, vol. 112, pages 192-197.